US5271230A - Liquid gas temperature control apparatus for and methods of depressing temperature to and maintaining it at a chosen depressed value - Google Patents

Liquid gas temperature control apparatus for and methods of depressing temperature to and maintaining it at a chosen depressed value Download PDF

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US5271230A
US5271230A US07/748,715 US74871591A US5271230A US 5271230 A US5271230 A US 5271230A US 74871591 A US74871591 A US 74871591A US 5271230 A US5271230 A US 5271230A
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coolant
chamber
temperature
flow
valve
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Lewis H. Spiess
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PerkinElmer Ltd
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PerkinElmer Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L7/00—Heating or cooling apparatus; Heat insulating devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B21/00—Machines, plants or systems, using electric or magnetic effects
    • F25B21/02—Machines, plants or systems, using electric or magnetic effects using Peltier effect; using Nernst-Ettinghausen effect
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D29/00—Arrangement or mounting of control or safety devices
    • F25D29/001—Arrangement or mounting of control or safety devices for cryogenic fluid systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/26—Conditioning of the fluid carrier; Flow patterns
    • G01N30/28—Control of physical parameters of the fluid carrier
    • G01N30/30—Control of physical parameters of the fluid carrier of temperature
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/1919—Control of temperature characterised by the use of electric means characterised by the type of controller
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
    • G05D23/24—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element having a resistance varying with temperature, e.g. a thermistor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/26—Conditioning of the fluid carrier; Flow patterns
    • G01N30/28—Control of physical parameters of the fluid carrier
    • G01N30/30—Control of physical parameters of the fluid carrier of temperature
    • G01N2030/3023—Control of physical parameters of the fluid carrier of temperature using cryogenic fluids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/26—Conditioning of the fluid carrier; Flow patterns
    • G01N30/28—Control of physical parameters of the fluid carrier
    • G01N30/30—Control of physical parameters of the fluid carrier of temperature
    • G01N2030/3084—Control of physical parameters of the fluid carrier of temperature ovens

Definitions

  • This invention relates to temperature control, both in terms of systems and methods, intended for lowering the temperature of an enclosure or partial enclosure and/or any objects within it from a higher actual value to a desired lower value and maintaining it substantially constant at the desire lower value for any required periods by flowing through the enclosure a liquefied gas in either the liquid or the vaporized state as the application demands.
  • the cooling effect of the liquefied gas which is drawn from a suitable storage container, is determined by controlling the rate at which it flows through the enclosure and the rate at which it is dissipated, e.g. to atmosphere, via a venting orifice, the two rates being so coordinated in response to the temperature sensed within the enclosure as to attain and -maintain the desired lower temperature.
  • the term “lower” in the phrase “the desired lower temperature”, or the equivalent phrase “the desired lower value” following a prior mention of the term “temperature”, shall be construed with reference to an assumed “actual higher temperature”, e.g. if an object is at 50° C. and it is required to cool it down to 5° C., the former value is the “actual higher temperature” and the latter the “desired lower temperature”.
  • the use of a liquefied gas coolant does not necessarily mean that the desired lower temperature is a sub-zero temperature.
  • liquid gas e.g. liquid helium
  • Liquid nitrogen which is readily available at a comparatively low cost, is particularly suitable as a cooling medium (hereinafter coolant) in many applications where the temperature of the enclosure and/or any objects within it must be depressed down to -100° C. or lower from a higher temperature; but even where the desired lower temperatures are not extreme, or, indeed, are above zero, liquid gas cooling may be indicated if high cool-down rates are required. If both high rates and very low temperatures must be attained, there are almost no practical alternatives, especially if high thermal capacitances are also involved.
  • coolant a cooling medium
  • liquid nitrogen as a coolant, but that shall not detract from the generality of suitable liquid gases that could be used as alternative coolants.
  • a problem encountered with liquid gas cooling is how to maintain a desired lower temperature within reasonably close limits, say, 1° C., when virtually the only expedient form of control is achieved by regulating the flow of the coolant, which flow is itself subject to variables, some of which are unpredictable. Before dwelling on the problem, it may be helpful to review briefly the construction of the vessel in which liquid gases are commercially supplied.
  • this product is made available commercially in a rather large stainless steel storage container called a Dewar (hereinafter the Dewar) which comprises an inner cylinder suspended from its top end within and spaced from an outer cylinder, the interspace being evacuated for good thermal insulation in order to minimize heat flow from ambient and keep vaporization of the liquid nitrogen within acceptable limits.
  • a Dewar hereinafter the Dewar
  • a manifold into which are screwed taps is provided at the top of the Dewar: one, the supply tap, communicates with a long narrow pipe reaching close to the bottom of the inner cylinder and is intended for supplying liquid nitrogen to a utilization circuit; the other communicates with a short pipe which only reaches just beyond the upper end wall of the inner cylinder and serves to draw vaporized liquid nitrogen instead, if so required by the user, apart from enabling the user to pressurize the Dewar with nitrogen gas to a pressure between 20 and 25 p.s.i. (i.e. between approximately 137 and 172 Kilopascals), unless self-pressurization has been provided for by the manufacturer of the Dewar.
  • Dewar pressure The pressure exerted by the vaporized liquid gas within the Dewar which bears on the liquid gas and forces it up the long pipe towards the supply tap shall hereinafter be referred to as Dewar pressure.
  • a blow-off valve venting to atmosphere prevents any excess pressure building up.
  • the user may in addition reduce the Dewar pressure by venting the coolant through the second mentioned tap.
  • a thermally insulated pipe of suitable length and bore is used that is usually referred to as a "transfer line". If the coolant in the transfer line has been static or flowing at a low rate for some time, the coolant will be in the vaporized state because under such conditions the cooling will not be adequate to maintain the liquid state against the warming effect on the coolant of ambient heat leaking through the thermal insulation of the transfer line. It follows that after first opening the supply tap of the Dewar the coolant may issue from the transfer line in the vaporized state until an appropriate coolant rate has been maintained long enough to cool down the transfer line to the point where vaporized gas is replaced by liquid gas.
  • the time required for the change over will depend on the flow rate. In fact, in all but the most demanding applications it is possible to switch over to vaporized liquid gas cooling by so adjusting the coolant rate that at a given ambient temperature it just fails to cool the transfer line sufficiently to effect the change over.
  • the transfer line may be supplied by the manufacturer of apparatus in which liquid gas cooling is utilized. Its characteristics will therefore be such as to allow the coolant flow rate to reach the maximum value likely to be required at the point of connection to the utilization circuit, assuming a standard Dewar pressure, such as between 20 and 25 p.s.i.. Of course, non-standard transfer lines and Dewar pressures may be substituted if desired and the coolant flow rate adjusted accordingly.
  • cooling an enclosure requires a flow of coolant to be maintained through the enclosure. If we assume that a given maximum flow rate will be required to achieve a reasonably fast initial cool-down to the lowest temperature in the design range of a cooling system, that flow rate may be maintained continuously until the required temperature has been attained and thereafter on an intermittent basis via controlling means responsive to a temperature sensor within the enclosure, said means being adapted to ensure that the cooling effect is just adequate to balance the effect of heat transfer from ambient.
  • the coolant is passed through a solenoid valve which is either fully open or fully closed, depending on a command signal responsive to the temperature sensor.
  • a command signal responsive to the temperature sensor.
  • the object of the present invention is to provide temperature control systems and methods utilizing liquid gas as a coolant for lowering the temperature within a complete or a partial enclosure and/or the temperature of any objects therein from a higher actual value to a desired lower value which are characterized by smaller consumption of coolant, closer approximation to the set desired lower temperature, less noise, and less wear and tear of the controlling parts compared with known systems and methods.
  • the said object is essentialy achieved by providing two electrically operated coolant valves instead of the customary single valve, one valve being a coolant supply valve and the other a coolant venting valve, through which valves the flow of coolant is metered to the enclosure and a venting orifice, respectively, a microcomputer coordinating the operation of the valves.
  • a temperature control system for lowering the temperature within a chamber from a higher actual value to a desired lower value and maintaining it at said desired lower value by passing through the chamber a controlled flow of coolant available from a source of supply in the form of liquid gas, comprising:
  • a controller responsive to the temperature sensor and to the temperature setting means for controlling the means for automatically selectively supplying the coolant in order to bring the chamber and/or any object therein to and maintain it at the set desired lower value.
  • chamber in so far as the present invention is concerned shall refer to means for partially or totally enclosing a given space that is to be cooled to a desired lower temperature together with any object or objects located therein.
  • the chamber may be located within an ante-chamber which is intermediate between ambient and the chamber and is itself subjected to cooling, the coolant being arranged to flow first through the chamber proper and then through the ante-chamber.
  • the temperature within the chamber can then be controlled to fine limits because that of the surrounding ante-chamber does not greatly differ from it and thus acts as a particularly effective buffer against ambient temperature variations.
  • the temperature of the object need not track that of the chamber, such as when the temperature sensor is in close thermal contact with the object.
  • cooling circuit shall refer to the means through which the coolant is conveyed from the transfer line terminal for the purpose of lowering the temperature of the chamber to a desired lower value.
  • transfer line is not part of the "coolant circuit” in a system in accordance with the present invention, its characteristics are taken into account in the design and control of the coolant circuit.
  • the means for automatically selectively supplying coolant to the chamber and the venting orifice may comprise electrically controllable coolant supply valve and coolant venting valve, each having an input port and an output port.
  • the input port of the coolant supply valve may be adapted for receiving a liquid gas coolant from a supply Dewar through a transfer line and the output port may be connected to a coolant supply duct for conveying coolant to the chamber.
  • a coolant venting duct may be provided branching from the coolant supply duct and leading to the input port of the coolant venting valve, the output port of which either inherently or through an extension therefrom provides the venting orifice.
  • the controller may include a micro-computer responsive to dedicated software in determining the opening and closing of the two valves, each of which may be solenoid operated.
  • the micro-computer may be so conditioned by the software that during the initial cool-down of the chamber from the higher actual temperature to the desired lower temperature both the coolant supply valve and the coolant venting valve are kept open.
  • the impedance to coolant flow of the coolant supply duct and the coolant venting duct may be so arranged, in relation to given Dewar pressure and transfer line impedance, that the flow rate of coolant is just adequate for the initial cool-down of the chamber to the lowest temperature in the design range to be effected in an acceptable time.
  • the flow rate may be chosen to ensure that the coolant is in the vaporized state. Alternatively, a higher flow rate may be used to cause the coolant to flow in the liquid state for a shorter cool-down time.
  • the initial cool-down of the chamber takes advantage of the cumulative effect of coolant flow through the supply valve and the venting valve.
  • the flow through the venting valve tends to reduce the flow through the chamber, it in fact causes the coolant to be delivered to the chamber at a temperature lower than would otherwise be the case, with the result that the valves actually cooperate in depressing the temperature of the chamber at a satisfactory rate.
  • the end of the initial cool-down period is reached when the temperature within the chamber, or of any object to be cooled therein, as the case may be, has dropped to the desired lower value.
  • the transfer line, as well as the parts such as the coolant supply duct, the coolant venting duct, and the two respective valves which together with the chamber make up the coolant circuit lag behind at a higher temperature. This is due to the fact that the thermal transfer rate from and to the coolant is likely to be much lower at least in some of said parts than in the chamber, wherein said rate is readily optimized. It follows that there could be considerable time lag before the temperature control system as a whole approximated thermal equilibrium, the part of the coolant circuit suffering the lower transfer rate finally determining the extent of the delay.
  • the coolant supply valve may be kept open during the time the temperature control system is settling down towards thermal equilibrium following the initial cool-down in order to prevent some of the heat stored in the thermal capacity of the parts referred to from being dumped into the chamber and causing the temperature therein to rise.
  • the full cooling effect may now be reduced to ensure that the temperature of the chamber does not fall below the desired lower value. This may be taken care of by arranging (again, through the software) for the coolant venting valve to be closed and perhaps re-opened occasionally to combat incidental temperature rises during the settling down process.
  • the intervention of the venting valve will be for shorter and shorter periods, until at or near equilibrium it may be arranged, through the software, for the supply valve to take over control and operate intermittently so as just to compensate for heat leakage from ambient into the chamber. Occasional temperature disturbances causing the temperature to rise in the chamber may be counteracted whenever they occur, the software being made to provide for the momentary opening of the venting valve to augment the total coolant flow.
  • the flow rate of the coolant is preferably chosen so as to ensure that the coolant will never enter the coolant circuit in the liquid state. It has been found that the use of coolant in the vaporized state enables the desired lower temperature to be controlled to closer limits that would be possible by flowing the coolant in the liquid state.
  • the two-valve control as outlined in the present embodiment lessens the work load on the coolant supply valve, which after the initial cool-down is not required to control the coolant at maximum flow and at a high rate of intermittence.
  • the supply valve is only required to control a comparatively small coolant flow at moderate on/off rates.
  • the temperature control system outlined when compared with the prior art, enables a closer temperature control to be maintained with a lower consumption of coolant and much less hammering of the supply valve.
  • the venting valve is less heavily loaded, of course, because it would serve no purpose if it were to be opened when the supply valve was not open and at all events its on/off rate is always less than that of the supply valve which provides the main control of coolant flow.
  • the protruding parts of the heated injector and the heated detector represent a thermal capacity and a source of heat that together with the thermal capacity of such parts as the column and other fittings within the oven make up an aggregate thermal load that must be accounted for in terms of coolant flow.
  • the single solenoid valve enters the intermittent mode of operation referred to earlier, typically controlled by means for adjusting the duration of the open and closed periods of the valve in response to a temperature sensor located in the oven, the coolant reaching the single solenoid valve may unpredictably alternate between the liquid and the vaporized state, around the temperature corresponding to a threshold between the two. It has been realized that the ON period occurring whilst the coolant is in the liquid state is more effective than the same period when the coolant is in the vaporized state.
  • a heat exchanger through which the coolant must pass before reaching the means for automatically selectively supplying coolant to the chamber a-nd the venting orifice.
  • the heat exchanger may be in the form of a coolant vaporizing duct adapted to be connected to the output end of a transfer line from a Dewar and so constructed and arranged that at a predetermined maximum coolant flow rate any coolant approaching the upstream end of the coolant vaporizing duct in the liquid state will have vaporized by the time the coolant reaches the means for automatically selectively supplying coolant to the chamber and the venting orifice, the vaporizing heat having been supplied by the chamber.
  • the coolant vaporizing duct may be given any appropriate configuration to maximize heat transfer between the chamber and the coolant, even though a pipe of suitable length and bore may be adequate in certain applications. It should be noted that the heat transfer actually assists the cooling of the chamber and therefore tends to reduce coolant consumption.
  • means may be provided for setting up the venting orifice within the chamber.
  • first embodiment may be selectively included in the second embodiment.
  • advantages over the prior art realized in the first embodiment in terms of lower coolant consumption, closer temperature control and very much reduced valve hammering are reflected in the second embodiment.
  • the present invention in part springs from the realization that wherever the desired lower temperature permits it closer temperature control of the chamber after the initial cool-down can be achieved by flowing the coolant therethrough in the vaporized state.
  • the desired lower temperature is such that it can only be reached by flowing liquid gas in the liquid state, steps must be taken to ensure that the coolant is prevented from vaporizing in any part of the coolant circuit, thus avoiding some of the drawbacks of the prior art dwelled upon earlier.
  • fresh coolant in the liquid state must continuously replace the coolant in the transfer line and the coolant circuit which has suffered heat transfer from ambient, in order to prevent a temperature rise in both and possible formation of vaporized coolant. Note that when the coolant flow to the chamber is interrupted for temperature control purposes the coolant warms up if no by-pass flow is provided.
  • the means for automatically selectively supplying coolant to the chamber and the venting orifice may include a two-way controlled valve for routing liquid coolant from a transfer line either to the chamber or the venting orifice but not both at the same time.
  • the controller may include a microcomputer responsive to dedicated software.
  • the microcomputer may be so conditioned by the software that during the initial cool-down the two-way valve is switched to the chamber and, therefore, no coolant is vented through to the venting orifice.
  • the micro-computer may in addition be so conditioned that following the end of cool-down the desired lower temperature is maintained by intermittently switching the two-way valve between the chamber and the venting orifice so as to supply coolant to the chamber at such frequency as may be required to offset any heat transfer thereto, such as from ambient, tending to warm the chamber above the desired lower temperature.
  • the vaporization of the coolant may be prevented by ensuring that the cumulative effect of coolant flow through the two-way valve is sufficient to prevent critical warming up of the transfer line and the coolant circuit.
  • a two-way valve may be readily simulated by joining two identical solenoid valves with their bases in good thermal contact and commoning the two input ports such as by means of a manifold to which the transfer line is also connected.
  • the present invention has identified the fundamental problem that has prevented the prior art from providing a liquid-gas temperature control system that is satisfactory in terms of a) closeness of the controlled temperature achieved to the desired lower valve set by the operator, b) economical coolant consumption, c) acceptable valve life and d) tolerable noise, and has provided a simple and expedient solution thereto.
  • the fundamental problem is that the prior art has attempted to control flow during the temperature stabilization stage at the same maximum rate required for fast cool-down. This is the major reason for the poor results obtained by the prior art in terms of a) to d) as referred to hereabove.
  • the solution provided by the invention is to control both the supply of the coolant to the chamber within which an object is to be brought down to the desired lower temperature and the venting of the coolant through a venting orifice in response to the actual temperature of the chamber compared to the set lower temperature.
  • the means for automatically selectively supplying coolant to the chamber are all able to operate under vastly reduced loading, which enables great improvements to be realized in terms of a) to d) as aforesaid.
  • the invention has also identified a subsidiary problem, associated with the changing physical state of the coolant, which has a major bearing on the closeness of temperature control that may be achieved: the widely differing effectiveness of the control action depending on whether the coolant is flowing through in the vaporized state or the liquid state.
  • the solution to the subsidiary problem may be expressed in the context of each of the following three situations:
  • the first situation is expediently met by pre-arranging the temperature control system for use of vaporized liquid gas throughout the entire temperature control operation involving an initial fast cool-down stage and a subsequent temperature stabilization stage at the desired lower value, although, somewhat less expediently, liquid coolant might be used during cool-down if exceptionally fast cool-down rates must be attained; the second, by ensuring that the coolant is prevented from flowing through the coolant circuit in the liquid state, at least during the temperature stabilization stage; and, finally, the third by preventing the formation of vaporized coolant during both the cool-down and the temperature stabilization stage.
  • flow control during the temperature stabilization stage should be applied on the coolant on either the vaporized state or the liquid state but not a combination of the two states.
  • the advantage derived from the solution of the subsidiary problem are additive to those derived from the solution of the fundamental problem.
  • FIG. 1 is an introductory schematic representation of FIG. 2.
  • FIG. 2 is a representation of a basic practical embodiment of the invention from which other embodiments are derived.
  • FIG. 2A depicts a derived embodiment in an application of the invention to the cooling of a cold trap.
  • FIG. 2B depicts a detail of FIG. 2A.
  • FIG. 2C depicts a derived embodiment in which the cold trap of FIG. 2A is superimposed on a thermo-electric pump.
  • FIG. 3 is a schematic representation of a controller including a microcomputer through which the attainment and stabilization of the desired lower temperature is controlled in each of the embodiments hereof.
  • FIG. 4 is a flow chart of the temperature control operations performed by the microcomputer in response to dedicated software in each of the embodiments hereof with the exception of those described with reference to FIG. 6 and 7.
  • FIG. 5 is a representation of a derived embodiment in an application of the invention to a chromatographic oven.
  • FIG. 6 depicts a modification of the FIG. 2 embodiment enabling extreme desired lower temperatures to be attained and maintained by flowing liquid gas exclusively in the liquid state via a two-way valve.
  • FIG. 7 depicts the FIG. 6 modification with the two-way valve simulated by two identical solenoid valves joined base to base and the two input ports commoned by a manifold.
  • FIG. 8 is a flow chart of the operations performed by the microcomputer within the controller in response to dedicated software applicable to the modifications of FIGS. 6 and 7.
  • a temperature control system in accordance with the present invention comprises, in broad diagrammatic outline: an automatically controllable coolant supply valve in the form of solenoid valve 1; a chamber 2 arranged to allow a small leakage of coolant to atmosphere which is either inherent in the design (see FIG. 5) or introduced by means of a vent (see FIGS.
  • a coolant supply duct 3 comprising limbs 3A1 and 3A2 of a T-piece connector 3A and a pipe 3B joined to the limb 3A2, the limb 3A1 forming a direct connection with the output port (not shown) of solenoid valve 1 and the pipe 3B feeding into chamber 2;
  • a coolant venting duct comprising limb 3A3 of T-piece 3A joined to a pipe 4, including a coiled portion 4A to be exposed to warming air from a fan 4B, said pipe feeding into the input port (not shown) of a coolant venting valve in the form of solenoid valve 5, the output port of which represents or leads to a venting orifice (see FIG. 2); and a controller of solenoid valves 1 and 5 in the form of a microcomputer controller 6.
  • a temperature sensor 2B which is provided with a pair of leads (as will be shown later) extending to the controller 6.
  • the temperature sensor is advantageously a localized sensing device, preferably a thermocouple in good thermal contact with the object.
  • the temperature sensor is advantageously a diffuse device, preferably a platinum resistor sensor, located within the chamber but not in contact with any of the objects therein.
  • Reference 2B is therefore identified with a generic sensor where the situation admits of both specific sensors, such as in describing the temperature control system with reference to FIGS. 3 and 4, or is identified with one or other specific sensor where one is preferred to the other, such as in the description of FIGS. 2A, 2B, 2C and 5.
  • coolant supply valve 1 coolant venting valve 5
  • coolant supply duct 3 coolant venting duct 4 a-nd chamber 2
  • liquid nitrogen from a nitrogen Dewar (not shown) is fed to the input port (not shown) of valve 1 in the direction of arrow A and, when valve 1 is open, is conveyed through limbs 3A1, 3A2 and pipe 3B to chamber 2, from whence it is allowed to leak to atmosphere in the direction of arrow B through a vent or simultaneously from a number of inherent leakage points, after having diffused throughout the chamber 2.
  • coolant is passed to the input port of solenoid valve 5 via limbs 3A1 and 3A3 and pipe 4, with the result that when valve 5 is open some coolant will vent through the output port (not shown) of valve 5 to atmosphere, in the direction of arrow C.
  • Solenoid valve I is supported on a flange 9A of a frame 9 via a thermally insulating slab 10 retained by screws applied from the underneath of the flange 9A and, therefore, not seen in FIG. 2.
  • the output port 1B of solenoid valve 1 is connected to the limb 3A1 of T-piece 3A and the coolant supply duct 3 (FIG. 1) is completed through the connection of pipe 3B to the limb 3A2 via a pipe union 3B1.
  • Pipe 3B is thermally insulated by resilient sleeve 3B2, which penetrates the chamber 2 and forms a seal therewith at the point of entry.
  • Limb 3A3 of T-piece 3A is connected to pipe 4, including coiled middle portion 4A, by means of a pipe union 4C.
  • a similar connection is established at the downstream end of pipe 4, involving engagement between a pipe union 4D and an adapter 5A1, screwed into the input port 5A of solenoid valve 5, the latter being supported on a bracket 9B, integral with frame 9, by means of screws 9B1 and 9B2.
  • Adaptor 5B1 and pipe union 11A cooperate in like manner to make a connection between venting pipe 11 and the output port 5B (hidden from view) of valve 5.
  • the end 11B of pipe 11 represents the venting orifice. If the pipe 11 is omitted, the output port 5B acts as the venting orifice.
  • the frame 9 retains a drip tray 12 by a lower angled extension 9C provided with upturned retaining flanges such as 9C1 and 9C2.
  • the dip tray 12 is preferably a plastics tray and serves the purpose of collecting drips, from the coolant circuit above it, resulting from the surface frost formation due to ambient humidity, when the circuit is operative, and the subsequent defrosting, when it is turned off.
  • valve 1 The main operational requirement of valve 1 is that it be capable of performing satisfactorily at temperatures well below -100° C.
  • the same requirement has been circumvented in the case of valve 5 by providing the coiled portion 4A in pipe 4 and causing warming air from fan 4B to impinge on the said portion.
  • Fan 4B as depicted in FIG. 2 is a well-known readily available 5-bladed fan with in-built electric motor.
  • the hub of the fan is integral with the rotating part of the motor marked by a circular arrow D denoting the direction of rotation.
  • the stationary part faces the coiled portion 4A and it is not seen; it is linked to a supporting frame by struts.
  • the struts and the frame have been omitted because they would have largely obscured the view of the coiled portion 4A.
  • the motor is energized from an alternating power supply, such as the public supply, marked by the symbol shown, via leads 4B1 and 4B2.
  • the temperature control system is part of an apparatus in which heat is generated and an extractor fan is already provided, it is simply a matter of arranging the coiled portion to be located in the exhaust stream of the fan.
  • FIG. 2 it is assumed that the fan is already available to extract heat from the apparatus of which the temperature control system is a part. If that is not the case, and for any design reason it would be inconvenient to provide a warming fan, the obvious alternative is to omit the coiled portion 4A in pipe 4 and fit a valve 5 which meets the same specification as that of valve 1.
  • the chamber 2 may assume any required shape and proportions, depending on its purpose and the configuration of the object or objects to be cooled within it.
  • the parallelepipedal aluminium box depicted in FIG. 2 is purely symbolical, therefore, of any convenient shape and size.
  • valve I and valve 5 are connected to the controller 6 via respective lead pairs 1C1-1C2 and 5C1-5C2.
  • Another pair of leads, 2B1-2B2 connect the temperature sensor 2B to the controller 6 which is energized from a 24-Volt direct current power supply marked DC, via leads S1 and S2.
  • chamber 2 may house a single object the temperature of which is to be closely controlled, in which case the temperature sensor 2B is preferably a thermo-couple welded to the object; or it may house several objects and the temperature of the enclosed space is to be sensed for practical reasons, in which case the temperature sensor is preferably a coiled resistance comprising many turns of very fine platinum wire.
  • the temperature sensor 2B is preferably a thermo-couple welded to the object; or it may house several objects and the temperature of the enclosed space is to be sensed for practical reasons, in which case the temperature sensor is preferably a coiled resistance comprising many turns of very fine platinum wire.
  • the temperature sensor does not significantly affect the operation of the controller 6, said operation will now be described on the basis that the temperature sensor may be of either kind.
  • FIGS. 3 and 4 The description of FIGS. 3 and 4 that follows applies to the embodiments of FIG. 2 and derivations therefrom, except that the embodiments of FIGS. 6 and 7 require a software modification in accordance with the flow chart of FIG. 8.
  • the controller 6 represented by the parts within the outer dotted frame, receives an input from the temperature sensor 2B (FIG. 2) and causes energizing outputs to the solenoids within solenoid valves 1 and 5, respectively, to be delivered or interrupted, depending on whether the valves are to be opened or closed.
  • the output of the temperature sensor 2B is amplified by amplifier 6A, changed to digital form by the analogue-to-digital converter 6B, and extended to the microcomputer 6C via a bus 6D communicating with a read-only-memory (ROM) 6C1, a microprocessor 6C2, and a read-and-write memory (RAM) 6C3.
  • ROM read-only-memory
  • RAM read-and-write memory
  • the bus 6D also communicates with a keypad 6E, enabling the user to set the desired lower temperature, and a display 6F which shows both the temperature demanded and that actually achieved by the temperature control system.
  • the computed output as determined by a software program stored in the ROM 6C1 is extended to the latch 6G which branches into two channels, one for controlling the valve 1 and the other for controlling the valve 5.
  • the first named channel comprises a driver 6H1 providing sufficient power to operate a relay 6I1, which, in turn, operates the solenoid in valve 1.
  • the second channel comprises likewise driver 6H2 and relay 6I2 operating the solenoid in valve 5.
  • each of valves I and 5 is open or closed is determined by the software program stored in the ROM 6CI, which compares to the signal from the temperature sensor 2B with the desired lower temperature set on the keypad 6E and conditions the microcomputer 6C to operate the latch 6G and control the solenoid in valve 1 via driver 6H1 and relay 6I1 and the solenoid in valve 5 via driver 6H2 and relay 6I2 to establish the coolant flow conditions that will cool the chamber 2 to the set temperature.
  • conventional solenoid valves admit of only two states: fully open, when energized, and fully closed, when deenergized, although the inverse status may be arranged if required.
  • the program stored in the ROM 6C1 actually implements the requirements set out in the flow chart of FIG. 4, which shall now be described in detail.
  • the first valve control operation commanded by the program occurs in the manner specified at 6C1D, whereby both solenoid valves 1 and 5 are fully opened to enable a rapid cool-down of the chamber 2 and its contents from ambient temperature to the set desired lower temperature. While the cooldown is in progress, the temperature within the chamber 2 is sensed by the temperature sensor 2B and, under software control, is compared with the set value stored in the RAM 6C3 to establish first whether, in accordance with 6C1E, the actual temperature within the chamber 2 is higher than the desired lower temperature (represented by -X) lowered by 0.25° C., e.g. assuming the set temperature to be -100, is the actual temperature higher, i.e. warmer, than -100.25?
  • valve 1 be kept open and valve 5 be closed. This means that the cooling effect is being reduced, although the flow of coolant through the chamber 2 is being maintained and it is in fact slightly increased, but at a higher temperature since valve 5 is not assisting in maintaining a high total flow made up of chamber flow and venting flow and as a result the coolant conveying parts affected by ambient temperature will start to warm up slightly.
  • FIG. 2 The embodiment so far described with reference to FIG. 2, FIG. 3 and FIG. 4 may be adapted for specific applications, some of which will determine the shape, size and other physical characteristics of the chamber 2.
  • no vent is required to allow the coolant to flow through because the enclosure acting as a chamber is almost inevitably leaky, e.g. the oven of a gas chromatograph.
  • a vent with or without a non-return valve is desirable, e.g. in the housing of a cold trap.
  • the chamber 2 in FIG. 2 is symbolical of both situations, as will be presently appreciated.
  • chamber 2 may house a cold trap comprising in essence a cylindrical tube containing an adsorbent in which a gaseous analytical sample is trapped whilst the temperature of the tube is maintained at a desired lower value over an extended period, followed by a very short interval during which the temperature is raised to a comparatively high value to effect thermal desorption of the sample in the form of a "plug" concentrated in time, typically for injection into the column of a gas chromatograph.
  • a cold trap comprising in essence a cylindrical tube containing an adsorbent in which a gaseous analytical sample is trapped whilst the temperature of the tube is maintained at a desired lower value over an extended period, followed by a very short interval during which the temperature is raised to a comparatively high value to effect thermal desorption of the sample in the form of a "plug" concentrated in time, typically for injection into the column of a gas chromatograph.
  • FIG. 3 of the said patent the cylindrical tube is represented by the U-tube 1, which is adapted for ohmic heating, cooperates with the thermo-electric pump 7 and is contained within a housing 9 that is readily adapted in accordance with the present description to act as a chamber 2 (FIG. 2) to depress the U-tube 1 well below the sub-zero temperature attainable with the thermo-electric pump 7.
  • the chamber 2 as shown in FIG. 2 hereof may replace the housing 9 in FIG. 3 of the imported patent with the addition of a vent which is in essence a suitably sized orifice in a wall of chamber 2 or the vent 2A referred to in the description of FIG.
  • thermo-couples 1B1 and 132 could be shared by controller 6 of FIG. 3 and 4 hereof, a further thermo-couple also welded to the U-tube 1 is preferred to facilitate superimposition of the system in accordance with the present invention without interfering with the existing temperature control provided in the imported patent.
  • the present invention is well suited to meeting the requirements of cold trap applications even more demanding than the one just referred to.
  • the thermal capacity of the trap tube must be reduced to a minimum and any extra thermal capacity such as of heat exchangers and the like that might be required for the purpose of liquid gas cooling could not be tolerated, since it would lengthen the heating cycle and therefore extend the period over which the "plug" was formed, thus spreading the length of the plug within the column and spoiling the resolution of the chromatogram
  • the arrangement of FIG. 2A is particularly advantageous.
  • FIG. 2A the chamber 2 of FIG. 2 is shown ghosted.
  • the jacket 2D surrounds a straight, cylindrical, thin-walled, stainless steel tube 2C of very low thermal capacity and between the inner wall of the jacket 2D and the outer surface of the tube 2C extends an annular chamber 2D3 the width of which is determined by three projections 2D4 acting as spacers of tube 2C from the inner cylindrical surface of the jacket 2D.
  • the upper half 2D1 of jacket 2D is provided with two nipples, 2D1A and 2D1B, to which branches 3B3A and 3B3B of pipe 3B are respectively connected by T-piece 3B3C.
  • the said nipples allow the coolant to reach the chamber 2D3, swirl around the tube 2C and escape into the ante-chamber 2 through both longitudinal ends of the chamber 2D3, which ends are left open except for the small obstruction caused by the projections 2D4. They are longitudinally spaced to provide a better distribution of the coolant around the central region of the tube 2C, where the adsorbent is located.
  • the ante-chamber 2 is protected against ingress of ambient moisture both by sealing its lid and pumping dry nitrogen into it via a through pipe 2E cooperating with a grommet 2E1 to guard against small leaks from ambient by maintaining a positive gas pressure within the ante-chamber even when the coolant supply valve 1 is closed.
  • the ante-chamber is provided with a vent 2A fitted with a non-return valve which opens when the pressure within the chamber reaches 0.5 p.s.i. (pounds per square inch). Any moisture trapped within the ante-chamber would have a deleterious effect on the performance of the cold trap since it would amount to a large added thermal capacity that could not be tolerated where it was a design requirement that the overall thermal capacity had to be reduced to a minimum.
  • Tube 2C contains a suitable adsorbent (not shown) and is provided with two welded leads 2C1 and 2C2 by which the central tube region may be raised rapidly to an elevated temperature by the ohmic heating resulting from passing a heavy current therethrough, via the said leads, from an AC (alternate current) source of supply via step-down transformer T, the primary of which is energized through a switch SW1.
  • the temperature sensor 2B (FIG.
  • thermo-couple 2B in the form of a thermo-couple, is actually welded to the tube 2C close to its central region, the thermo-couple leads 2B1 and 2B2 passing through an aperture 2D1C in the jacket half 2D1 and extending to the controller 6 (FIG. 2).
  • a gas sample may be conveyed to the tube 2C through a pipe 2C3 and after thermal desorption may be transferred to the chromatographic column of a gas chromatograph (not shown) via pipe 2C4.
  • the ante-chamber 2 is fitted with sealing grommets 2C3A and 2C4A where pipes 2C3 and 2C4 are fed through.
  • the lowest temperature that may be selected is -100° C.
  • the volume of the chamber 2D3 is 1 cc.
  • the combined thermal capacity of the tube 2C and the jacket 2D is indicated by the fact that the cool-down time from ambient to -100° is only 90 seconds and the coolant flow required to achieve it is quite moderate.
  • the impedances to flow of the various constituents of the cooling circuit have been so chosen that at the maximum value of coolant flow required to achieve the desired cool-down time no liquid nitrogen can ever reach the input port of valve 1 and that of course means that all other parts of the cooling circuit downstream of valve 1 must be free of liquid nitrogen, which once vaporized cannot be re-liquefied without subjecting it to very high pressure in a proper liquefying plant.
  • FIGS. 2-2A is particularly apt where cold trap requirements are such that for the most part they can only be met by liquid gas cooling.
  • FIG. 2C the jacket 2D as depicted in FIG. 2A has been fitted within the chamber 2 of FIG. 2, which chamber is now acting as an ante-chamber and is shown ghosted.
  • the referencing of parts in FIG. 2A will not be repeated in the like parts of FIG. 2C, with the exception of reference 2A.
  • the electrical connection between the trap tube 2C and the transformer T will not be shown.
  • the jacket 2D is shown mounted on the top stage 2F1 of a multi-stage, series-connected, thermo-electric pump 2F having leads 2F7A and 2F7B passing through grommet 2F7C and extending to stabilized DC power supply PS fed from an AC public supply through a switch SW2.
  • Stage 2F1 is in turn supported by an aluminium slab 2F2, which bears on stage 2F3, in turn supported by slab 2F4.
  • the third stage 2F5 is not seen. It lies between the slab 2F4 and the flat top 2F6A of a heat sink block 2F6 which top acts as the floor of the ante-chamber 2, shaped in the form of a hood the base rim of which rests on the heat sink 2F6 and is sealed thereto.
  • the ante-chamber 2 is fitted with a vent 2A as in the case of the ante-chamber 2 in FIG. 2A.
  • Slab 2F4 is provided with four lugs 2F4A for securing the entire stack to the top 2F6A of the heat sink 2F6 by means of nylon screws 2F4B.
  • slab 2F2 is secured to slab 2F4 by cooperating lugs 2F3A and nylon screws 2F3B.
  • the jacket half 2D2 (FIG. 2A) is secured to the slab 2F3 by nylon screws 2D2A.
  • thermo-electric pump 2F in cooperation with the heat sink 2F6 is well known and is touched upon in the imported patent. It is independent of the operation of the liquid gas temperature control system and gives the user the option of attaining the desired lower temperature either by means of the thermo-electric pump or the liquid gas system down to say -50° C. or overriding the thermoelectric pump down to -100° C.
  • FIGS. 2-2C fits a situation where a thermo-electric pump will normally serve, but often the cooling demands can only be met by using liquid gas as a coolant.
  • the temperature control system in accordance with the invention may advantageously form part of an accessory to a thermo-electric pump system.
  • thermo-electric pump 2F thermo-electric pump 2F
  • the fan 4B FIG. 2
  • FIG. 2 refers to an embodiment in which the arrangement within chamber 2 is generalized so that, by specifying different arrangements, embodiments may be derived all of which share in all other respects the construction and operation as described with reference to FIG. 2.
  • FIG. 2 in conjunction with FIG. 3 of the imported patent refers to a first derived embodiment in which a temperature control system in accordance with the present invention may be superimposed on the cold trap described in the said patent, so that either system may be used independently of the other or with the present system overriding the old system.
  • FIG. 2A and 2B refer to a second derived embodiment wherein the chamber 2 functions as an ante-chamber to a chamber proper within it, which has very low volume and thermal capacity and forms part of a cold trap with a particularly fast thermal response.
  • FIG. 2 and FIG. 2C relate to a third derived embodiment wherein liquid cooling in accordance with the second derived embodiment is superimposed on thermo-electric cooling as in the first derived embodiment.
  • FIG. 5 the two-valve temperature control system as depicted in FIG. 2 has been slightly modified to make it suitable for operation in a situation where the chamber is of considerable volume and thermal capacity and, therefore, the possibility of the coolant reaching the supply valve 1 (FIG. 2) in the liquid state cannot be ruled out, as observed earlier.
  • the symbolical chamber 2 in FIG. 2 takes the form of a chromatographic oven 13 as part of a gas chromatograph (not shown).
  • the oven proper is a space of typically 10,000 cc capacity within a parallelepipedal box formed by five fixed walls: a top wall 13A, a bottom wall 13B, two side walls 13C and 13D, a rear wall 13E and a front wall 13F having runners 13F1 and 13F2 slidable, respectively, on rail 13D1 fixed to wall 13D and rail 13C1 (not seen) fixed to wall 13C.
  • the wall 13F is in effect a slidable door which when open allows access to the interior of the box, i.e. the oven 13, and when closed completes the oven 13 as a chamber thermally insulated from ambient to some extent, but inevitably permitting some heat transfer to take place in the form of leakage.
  • Gas chromatographic ovens are not normally hermetically sealed from ambient when the door is closed. In fact, the air leakage is such that no provision need be made for venting the coolant when liquid gas is used. Oven 13 is no exception and a structurally defined vent such as depicted in FIG. 2A is not required.
  • a chromatographic injector 13F3 and a chromatographic detector 13F4 Fixed to the door 13F is a chromatographic injector 13F3 and a chromatographic detector 13F4, the input end of a chromatographic column 13F5 being connected to the first and the output end to the second. It will be noted that the injector 13F3 and the detector 13F4 actually protrude into the oven space when the door 13F is closed.
  • FIG. 2 and FIG. 5 share a number of common parts. Like parts have therefore been given like references.
  • the control of the supply valve 1, through leads 1C1, 1C2 and the venting valve 5, through leads 5C1, 5C2, by the controller 6 is as described with reference to FIGS. 2, 3 and 4.
  • the transfer line from the Dewar is not connected to the coolant supply valve 1, direct.
  • the transfer line 7 is joined in operation to an internal coolant vaporizing duct 13G, which runs close to the rear of wall 3E and forms an almost complete loop following roughly the contour of said wall before ending in a pipe union 13G1 external of wall 13E by which it is connected to the input port of valve 1 via a short piece of angled pipe 13G2.
  • To the output port of valve 1 is connected one end of the vertical limb (as drawn) of a fabricated T-pipe 3A (the T-piece connector and adaptor of FIG.
  • FIG. 2 have been dispensed with to simplify the drawing in a congested area, although the reference 3A has been retained) the other end being connected to the coolant venting valve 5, which performs the sane function as valve 5 in FIG. 2 but is in fact physically identical with valve 1 in both FIG. 2 and FIG. 5.
  • the arrangement of FIG. 2 involving a venting valve of lower specification made possible by the action of the warming loop 4A has been omitted since at the high rate of coolant flow required in the chromatographic application it is more important to lower coolant consumption than to reduce the cost of the venting valve.
  • the horizontal (as drawn) limb 3B of T-pipe 3A is prolongated via external pipe union 3C1 into an extension pipe 3C within the oven 13.
  • the coolant supply duct comprising parts 3A1, 3A2 and 3B in FIG. 1 is defined by the lower half of the vertical limb of T-pipe 3A, the horizontal limb 3B, the union 3C1 and the extension pipe 3C in FIG. 5.
  • the coolant venting duct comprising parts 3A1, 3A3 and 4 in FIG. 1 is represented by the two vertical limbs of the T-pipe in FIG. 5.
  • a venting pipe 11 is connected to the output port of valve 5. It has been simplified compared with its counterpart in FIG. 2 and is seen to comprise an angled pipe 11B joined by external pipe union 11C1 to extension pipe 11C running for a predetermined length within oven 13, the end 11C2 of pipe 11C representing the venting orifice.
  • a temperature sensor 2B in the form of a coiled platinum resistance to which the temperature control system as described with reference to FIGS. 2, 3 and 4 responds, is also located within the oven adjacent wall 13C, in an advantageously chosen location for sensing the space temperature of the oven 13. It is provided with leads 2B1 and 2B2 by which it is connected to controller 6.
  • valve 5 is mostly closed, which means that valve 1 is actually operative on a reduced flow and that at such flow the coolant reaching valve 1 from the transfer line 7 is likely to be in the vaporized state due to the longer exposure to ambient heat of the slowly flowing coolant.
  • valve 1 by feeding valve 1 not directly from the transfer line 7 but indirectly via the coolant vaporizing duct 13G, the possibility is avoided of liquid gas reaching the coolant circuit when the coolant supply valve 1 is operating intermittently. The reason why may be expressed as follows:
  • the coolant vaporizing duct 13G is coupled to the considerable thermal capacity of the oven, heat being transferred thereto from the physical parts undergoing cooling therein. If we imagine the oven to be at ambient temperature at the start of the cool-down stage and that for a period of one half hour or so before the start no coolant has passed through the transfer line 7 connected to the Dewar, opening the valves 1 and 5 fully for maximum coolant flow does not cause liquid gas to enter the coolant vaporizing duct 13G since during the period when the coolant is static in the transfer line it vaporizes due to ambient heat transfer.
  • the coolant reaches the upstream end of the coolant vaporizing duct 13G in the liquid state, because the high coolant flow has caused sufficient cooling of the transfer line to prevent vaporization therein, it will have vaporized by the time it reaches the downstream end because of the heat transfer from the oven parts to the coolant flowing in the coolant vaporizing duct 13G, which close to the start of cool-down will be at its maximum.
  • the coolant absorbs less heat and yet the same maximum flow is being maintained to secure the cool-down rate required.
  • the thermal coupling between the coolant vaporizing duct 13G and the oven parts is not sufficient to ensure that any liquid gas arriving at the upstream end of the coolant vaporizing duct 13G is vaporized before it reaches the downstream end. It is therefore a design consideration that the coupling must be adequate to satisfy worst-case situations. In other words, the heat exchanging performance of the coolant vaporizing duct 13G must be sufficient to provide such coupling. This can be achieved in the embodiment of FIG. 5 by selecting the proper length and disposition of the coolant vaporizing duct 13G.
  • the coolant vaporizing duct 13G by absorbing heat from the oven parts, is actually assisting the cooling process by virtue of the fact that it acts as a heat exchanger.
  • the same can be said of course for the runs of coolant supply duct and venting pipe that are led into the oven, said runs being referenced 3C and 11C, respectively, in FIG. 5. This makes for greater efficiency in terms of a lower consumption of liquid gas.
  • the lowest selectable temperature has been fixed at -100° C. by design choice, as in the case of the FIG. 2A and 2C embodiments, but this should not be taken to mean that lower temperatures could not be accommodated.
  • the lowest temperature should be some 20 to 50 degrees higher than the liquefying temperature of the gas used as a coolant, which in the case of nitrogen is -196° C.
  • the volume of the oven 13 is approximately 10,000 cc and its effective thermal capacity is such that it takes approximately 500 watts to raise the temperature of the oven by one degree ° C./sec starting at ambient temperature.
  • the cool-down time from ambient to -100° C. is approximately 6 minutes.
  • a coolant vaporizing duct 13G made up of aluminium tubing having a bore of 7 mm, a wall-thickness of 1.2 mm and a length of 800 mm and disposed as shown in FIG. 5 is adequate in preventing any coolant in the liquid state from reaching the input port of the valve 1 when the oven is fully operational, with the re-circulating fan 13I running, the detector 13F3 and 13F4 initially heated to a temperature of 250° above ambient and the door 13F firmly closed, of course.
  • the coolant vaporizing duct 13G which towards the end of the cool-down stage may be exposed to an oven temperature close to the lowest selectable value of -100° whilst the coolant flow is still at its maximum, is much less likely to vaporize the coolant from its liquid state than if the same line were exposed to ambient temperature as the transfer line 7 is, but that is not so for a number of reasons.
  • the thermal coupling between the transfer line 7 and ambient is very weak, which means that the resistance to heat transfer is quite high and, given sufficient coolant flow, the coolant can readily reach the temperature at which it does not vaporize, almost regardless of what the ambient temperature might be under normal operating conditions, such as are found in a laboratory.
  • valve 1 Once the critical cool-down stage is over, and valve 5 is mostly closed whilst valve 1 passes a reduced coolant flow, one of the advantages of the two-valve control of the present invention comes to the fore and the likelihood of the coolant being found in the liquid state in the cooling circuit or indeed in the transfer line 7 itself becomes minimal. It is true that occasionally valve 1 and valve 5 are opened together again for short periods, after the temperature control system has settled down for say one half hour or so, to take care of incidental warming up, e.g.
  • FIG. 2A it was assumed that no significant thermal capacity could be added within the chamber 2D3. This is certainly the case if the adsorption at low temperature of a gas sample within tube 2C is to be followed by a fast thermal desorption cycle which is to raise the tube to an elevated temperature in a few seconds. In the case of a chromatographic oven, added thermal capacity is not so critical since such fast heating cycles are not realistic.
  • the embodiments of FIG. 2A and FIG. 5 deal with different problems. In the first, the emphasis is on close temperature control and avoidance of added thermal capacity; in the second, on adapting the fine temperature control of the first to large-volume cooling while avoiding the presence of liquefied gas in the coolant circuit during intermittent operation of the coolant supply valve 1. Both represent a distinct advancement on the single-valve control of the prior art.
  • liquid gas in the liquid state is contemplated both during the initial cool-down stage and the next following stage during which the temperature control system tends towards thermal equilibrium while the coolant is being supplied intermittently.
  • An electrically controllable two-way valve referenced 1A5 for a reason that will presently be explained, comprises a common input port 1A5A, receiving in operation liquid gas coolant in the liquid state from the transfer line 7 and separate output ports 1A5B and 1A5C, the first communicating with coolant venting pipe 11, having venting orifice 11B and the second with coolant supply duct 3, leading to chamber 2, provided with vent 2A and in-built non-return valve, as described with reference to FIG. 2A.
  • Valve 1A5 is under the automatic control of controller 6, the link L between them symbolizing an electrical connection.
  • the control is such that coolant in the liquid state is flowing continuously from port 1A5A either through a path leading to output port 1A5B (the venting path) or through that leading to output port 1A5C (the supply path), both paths being symbolized by dotted line.
  • the controller 6 activates the supply path and the liquid coolant flows continuously through the chamber and out through the vent 2A, until the chamber or an object therein has reached the desired lower temperature. Thereafter, the operation of the controller is such that the supply path leading to the chamber is operated intermittently, any ON period being determined by the time required for a volume of coolant to flow through the chamber that is sufficient to offset any rise in temperature caused by ambient heat transfer into the chamber. At the end of the aforesaid period the supply path is disabled and the venting path is enabled, the coolant being thus vented through the pipe 11. In other words a flow of coolant is being continuously maintained through one path or the other.
  • the impedance to flow of the coolant venting pipe 11 and the series combination comprising the coolant supply duct 3, the chamber 2 and the vent 2A are so chosen, if need by a process of trial and error, that the cumulative effect of the coolant flowing intermittently through one and other path is sufficient to prevent the liquid gas ever rising to the vaporizing temperature, with the result that a better temperature control may be achieved compared with the single valve operation of the prior art, wherein incidental vaporization vitiates temperature control for the reasons stated earlier.
  • consumption is markedly reduced. This can readily be appreciated by considering that during the supply phase the venting is cut off altogether. If no provision were made for controlling venting in relation to supplying coolant, venting would have to be maintained-continuously during both the ON and the OFF phases of the coolant supply to the chamber.
  • FIG. 7 shows how a two-way valve may be readily simulated by means of valve 1 and valve 5 as depicted in FIG. 5, wherein the valves are of identical construction.
  • the ports bearing bases of the two valves are simply joined together in good thermal contact, and the adjacent input ports 1A and 5A are manifolded together by manifold M, to which is also connected the transfer line 7.
  • manifold M manifold M
  • the controller shown in FIG. 6 and FIG. 7 (in the latter the electrical leads from valves 1 and 5, respectively, to the controller 6 are symbolized by LL1 and LL2) is identical with the one described in FIG. 3, except that the software conditioning the microcomputer 6C implements different commands, as shown in the flow chart of FIG. 8.
  • a temperature sensor 2B within the chamber 2 feeds into the controller 6 as in FIGS. 1 and 2.
  • steps 14A, 14B and 14C conform to the first three steps in FIG. 4.
  • the microcomputer forming part of controller 6 is conditioned to enable the supply path of the two-way valve 1A5 of FIG. 6 and to keep the venting path disabled, thus initiating the cool-down stage of the chamber 2.
  • the waiting loop represented at 14E ensures that the cool-down continues as long as the temperature is higher than the desired lower temperature -X, the minus sign having the same meaning as defined with reference to the flow chart of FIG. 4.
  • 14F is another waiting loop to keep the cool-down on until the actual temperature is some 1.5 ° C. below the desired lower temperature, when the supply path (SP) of valve 1A5 is closed and the venting path (VP) is opened as indicated at 14G.
  • the waiting loop of 14H maintains the two-way valve 1A5 in the condition stated at 14G for as long as the actual temperature is some 10° C. below the desired lower value. If the temperature rises above -(X+10), the entire control operation starting from 14D is reiterated.
  • the temperature control is not as close as when the desired lower temperature is sufficiently high to enable vaporized coolant to be used. This is largely due to the fact the temperature of liquid gas in the liquid state varies within a very short range compared with that of vaporized liquid gas. This is a main reason why temperature control by vaporized coolant is preferable, in accordance with the present invention, where extreme desired lower temperatures are not involved.

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Cited By (8)

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Publication number Priority date Publication date Assignee Title
US20070023536A1 (en) * 2005-06-13 2007-02-01 Colin Baston Methods and apparatus for optimizing environmental humidity
US20070181208A1 (en) * 2006-02-06 2007-08-09 Honeywell International Inc. System and method for preventing blow-by of liquefied gases
WO2007109027A1 (en) * 2006-03-20 2007-09-27 Temptronic Corporation Temperature-controlled enclosures and temperature control system using the same
US20090188270A1 (en) * 2004-01-07 2009-07-30 Shinmaywa Industries, Ltd. Ultra-low temperature freezer, refrigeration system and vacuum apparatus
US20110039219A1 (en) * 2008-04-28 2011-02-17 Ersa Gmbh Device and method for thermally treating workpieces in particular by convective heat transfer
CN107940853A (zh) * 2017-11-14 2018-04-20 北京卫星环境工程研究所 用于热沉调温***的气氮调温单元
CN109283266A (zh) * 2017-07-21 2019-01-29 株式会社岛津制作所 冷媒导入装置以及气相色谱仪
CN110621994A (zh) * 2017-05-09 2019-12-27 株式会社岛津制作所 气相色谱仪

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005207662A (ja) * 2004-01-22 2005-08-04 Shin Meiwa Ind Co Ltd 超低温冷凍装置
KR102366006B1 (ko) * 2017-06-20 2022-02-23 삼성전자주식회사 오븐

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3271970A (en) * 1962-10-29 1966-09-13 Pennsylvania Wmb Inc Insulated cold storage rooms or similar enclosures
US3315474A (en) * 1965-08-23 1967-04-25 Farer Irving Mobile thermoelectric refrigeration system
US3512370A (en) * 1967-03-14 1970-05-19 Tom H Murphy Combined liquid gas-mechanical freezing process and apparatus therefor
US3705500A (en) * 1969-10-22 1972-12-12 Union Carbide Corp Nitrogen spray refrigeration system for perishables
US3714793A (en) * 1971-01-18 1973-02-06 Union Carbide Corp Intransit liquefied gas refrigeration system
US4041725A (en) * 1976-03-04 1977-08-16 Galt Equipment Limited Control system for refrigeration unit
US4576010A (en) * 1983-10-18 1986-03-18 Nhy-Temp, Inc. Cryogenic refrigeration control system

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1352976A (fr) * 1963-01-09 1964-02-21 Commissariat Energie Atomique Perfectionnements apportés aux moyens d'obtention et de régulation de températures, notamment de basses températures, dans une enceinte
DD101235A1 (de) * 1972-12-20 1973-10-20
GB2085309B (en) * 1980-10-10 1984-02-15 Perkin Elmer Ltd Concentrating gas component by condensation
IT1200592B (it) * 1985-02-22 1989-01-27 Erba Strumentazione Metodo e dispositivo per regolare la temperatura di raffreddamento di una trappola per campioni in un'apparecchiatura di analisi gascromatografica
US4780116A (en) * 1987-11-20 1988-10-25 Cheh Christopher H Low temperature preparative gas chromatography apparatus

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3271970A (en) * 1962-10-29 1966-09-13 Pennsylvania Wmb Inc Insulated cold storage rooms or similar enclosures
US3315474A (en) * 1965-08-23 1967-04-25 Farer Irving Mobile thermoelectric refrigeration system
US3512370A (en) * 1967-03-14 1970-05-19 Tom H Murphy Combined liquid gas-mechanical freezing process and apparatus therefor
US3705500A (en) * 1969-10-22 1972-12-12 Union Carbide Corp Nitrogen spray refrigeration system for perishables
US3714793A (en) * 1971-01-18 1973-02-06 Union Carbide Corp Intransit liquefied gas refrigeration system
US4041725A (en) * 1976-03-04 1977-08-16 Galt Equipment Limited Control system for refrigeration unit
US4576010A (en) * 1983-10-18 1986-03-18 Nhy-Temp, Inc. Cryogenic refrigeration control system

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090188270A1 (en) * 2004-01-07 2009-07-30 Shinmaywa Industries, Ltd. Ultra-low temperature freezer, refrigeration system and vacuum apparatus
US20070023536A1 (en) * 2005-06-13 2007-02-01 Colin Baston Methods and apparatus for optimizing environmental humidity
US20070181208A1 (en) * 2006-02-06 2007-08-09 Honeywell International Inc. System and method for preventing blow-by of liquefied gases
CN101443720B (zh) * 2006-03-20 2012-01-11 天普桑尼克公司 温度控制密封件和使用其的温度控制***
US20070240448A1 (en) * 2006-03-20 2007-10-18 Temptronic Corporation Temperature-controlled enclosures and temperature control system using the same
US7629533B2 (en) 2006-03-20 2009-12-08 Temptronic Corporation Temperature-controlled enclosures and temperature control system using the same
US20100043485A1 (en) * 2006-03-20 2010-02-25 Temptronic Corporation Temperature-controlled enclosures and temperature control system using the same
US10060668B2 (en) 2006-03-20 2018-08-28 Temptronic Corporation Temperature-controlled enclosures and temperature control system using the same
WO2007109027A1 (en) * 2006-03-20 2007-09-27 Temptronic Corporation Temperature-controlled enclosures and temperature control system using the same
US8408020B2 (en) 2006-03-20 2013-04-02 Temptronic Corporation Temperature-controlled enclosures and temperature control system using the same
US9168604B2 (en) * 2008-04-28 2015-10-27 Ersa Gmbh Device and method for thermally treating workpieces in particular by convective heat transfer
US20110039219A1 (en) * 2008-04-28 2011-02-17 Ersa Gmbh Device and method for thermally treating workpieces in particular by convective heat transfer
CN110621994A (zh) * 2017-05-09 2019-12-27 株式会社岛津制作所 气相色谱仪
CN110621994B (zh) * 2017-05-09 2023-03-10 株式会社岛津制作所 气相色谱仪
CN109283266A (zh) * 2017-07-21 2019-01-29 株式会社岛津制作所 冷媒导入装置以及气相色谱仪
US11016064B2 (en) * 2017-07-21 2021-05-25 Shimadzu Corporation Refrigerant introducer and gas chromatograph
CN109283266B (zh) * 2017-07-21 2021-08-10 株式会社岛津制作所 冷媒导入装置以及气相色谱仪
CN107940853A (zh) * 2017-11-14 2018-04-20 北京卫星环境工程研究所 用于热沉调温***的气氮调温单元

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JPH05173649A (ja) 1993-07-13
GB9019485D0 (en) 1990-10-24
DE9110762U1 (de) 1992-01-09
DE4128881A1 (de) 1992-03-12
GB2248318B (en) 1994-11-02
JP3609836B2 (ja) 2005-01-12
ITRM910662A1 (it) 1992-03-07
ITRM910662A0 (it) 1991-09-04
DE4128881C2 (de) 2000-10-19
GB2248318A (en) 1992-04-01
IT1250774B (it) 1995-04-21

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